PAREXEL International (NASDAQ:PRXL) shares soared nearly 15% in early trading Wednesday morning, as investors celebrated the clinical research services company's improved second-quarter results. PAREXEL has indeed rebounded from its doldrums, but if you stack this company up against its competitors, it's clear that the firm still has work to do.

PAREXEL service revenue for the quarter increased 10.3% -- compared to the same period in the last fiscal year -- to $149.8 million. Earnings per share actually sank 17.4%, from $0.23 to $0.19, but that was due to a temporarily high tax rate. The operating earnings picture looked much better, jumping 41.3% to $10.6 million.

This boosted the company's operating margin to 7.1%, a nice improvement from the 5.5% that the contract research outfit reported in last year's fiscal second quarter. Nevertheless, the firm continues to lag behind competitors, including KendleInternational (NASDAQ:KNDL), which achieved operating margins of 10.7% in its most recently reported quarter, and ICON (NASDAQ:ICLR) whose operating margin in its recently reported second quarter was 10%. Part of PAREXEL's trouble is its North American segment, which continues to be a drag on business. The company is working hard to minimize the problem and now does 65% of its business outside the U.S.

On the surface, PAREXEL looks to be on solid ground for the future. Backlog increased 8.1% quarter over quarter and 17.2% on a year-over-year basis to $844.7 million. But PAREXEL's CEO, Josef von Rickenbach attributed the company's new business success, in part, to strong demand from small and emerging biopharmaceutical firms. These smaller players are often less-than-reliable customers, since they may live or die based on the success or failure of one or two drug candidates.

PAREXEL is doubtless in better shape than it has been in recent quarters, but investors should still approach the company with some caution.

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Fool contributor Brian Gorman is a freelance writer in Chicago. He does not own shares of any companies mentioned in this article.